*Actual and potential birth control and related strategies and tactics can be somewhat similarly categorized. Thus, in brief, beginning on the male line: preventing the marshalling of viable sperm (by castration or certain pharmacological agents); reducing the amount of sperm produced; preventing the release of semen (or of one of its necessary components, e.g. by vasectomy); modifying the rate or spatial distribution of release of semen (as in hypospadias, a usually developmental or traumatic condition in which the urethra opens on the underside of the penis, sometimes near its base); separating semen release in space or time from the susceptible ovum (e.g. continence, limiting intercourse to presumably nonfertile periods, coitus interrupts, and preventing a fertile ovum from being present when sperm arrive); separation by interposition of a material barrier (e.g. condoms, spermicidal creams, foams, jellies); increasing resistance of the ovum to penetration; making the ovum infertile, even if penetrate; prevention of implantation of the fertilized egg; abortion; and infanticide.